1. Technical Field
The invention relates to a method of mixing and extruding viscous materials, particularly relatively highly viscous or pasty materials, and to a gearbox, in particular to a superimposing gear drive, for transmitting high torque and/or high revolutions per minute to an output drive shaft without changing gears. The gearbox may particularly be used together with dispensing cartridges and mixer elements for mixing and dispensing multi-component dental impression materials.
2. Description of the Related Art
Dispensing devices with cartridges are often used in the field of dentistry for mixing and dispensing dental compositions of two or more components, such as impression materials, restoratives, adhesives, cements, etching gels, sealants and the like.
In one type of dispensing device that comprises an applicator and a cartridge, the applicator has a plunger that is advanced either manually by the user or automatically by a machine during a dispensing operation. Often, the plunger is received in an open end of the cartridge and bears against a piston within the cartridge. As the plunger is advanced to move the piston, the piston expels or dispenses a quantity of material through a front outlet opening of the cartridge.
The dispensing cartridge of such a device often comprises two compartments that are formed by two cylindrical bodies arranged in parallel to each other. Each compartment contains a specific component, usually either a base paste or a catalyst paste. These two components are pressed from their respective compartments out into a mixing area, or tip, where the components mix to form the required dental material. The pressure further urges the mixture out of the mixing tip so that the dental professional can use it as desired.
One type of such dispensing devices is an assembly (e.g., the Garant™ dispenser available from 3M ESPE AG) that includes a reusable, hand-operated applicator and a disposable cartridge. Another type of such dispensing device is an automatic dispensing system (e.g., Pentamix™ 2 available from 3M ESPE AG) that includes a motor-driven mixing unit and reusable and interchangeable cartridges. The mixing unit comprises a chamber for holding the cartridge, and two parallel, motor-driven plungers designed to plunge into two respective compartments of the cartridge and to exert high pressure on the viscous components contained therein. The motor drive for the plungers provides high torque to extrude the viscous or highly viscous components under high pressure into a mixing tip. Furthermore, the motor also provides a reasonably higher speed to rapidly move the plungers forward and backward within the cartridge when the viscous components are not being extruded. DC motors are generally used in such devices. For example, the motor drives the plungers into a first or “back” position for filling new components into the cartridge and/or inserting new cartridges of components into the machine. After refilling, the plungers are driven into a second or “initial” position, wherein the plungers are in direct or indirect contact with the component(s). When the plungers each contact a component, the resistance, and therefore the load, to the drive increases and a high load is applied to the driving gearbox and motor during the dispensing operation.
It is difficult to achieve both high torque at low speed, and also low torque at high speed, without changing gears. It is also difficult to achieve highly different speeds, e.g., differing by a magnitude of 100, using a linear drive of any kind without changing gears or using clutch-like devices. The changing of gears typically requires a complicated drive. Furthermore, it is very difficult or sometimes even impossible to change gears under load. Devices that can perform these functions can as a result be complicated and expensive.
Furthermore, highly viscous, multi-component mixtures, like dental impression materials, are produced using mixing devices in which the individual components of the mixture are simultaneously supplied from separate cartridge cylinders to a mixer. From the mixing area, the mixture is then dispensed from a front end. The mixer may be a static mixer or, preferably, a dynamic mixer having a rotary mixer element. Known dynamic mixers have at their rear end (inlet side) a central hexagonal opening for coupling to a drive shaft, which shaft rotates the mixer element of the mixer, and the drive shaft is preferably connected to a motor. Accordingly, it is desirable to use a drive unit which can drive also the dynamic mixer in addition to moving the plungers.
It would be desirable to overcome these and/or other disadvantages of known gearboxes and methods of mixing and extruding viscous materials.